The present invention concerns improvements in negative dobbies for forming the warp shed in weaving looms. The object of these improvements is to reduce the stresses on some of the machine components and to obtain a more precise control of the heald frames, so as to allow a more efficient and rational use of the dobby in combination with looms working at high and very high speeds, as those already in use and now increasingly expanding.
In technique there are known to be negative dobbies for looms, wherein the engagement between the hooks pivoted on the rockers and the respective crooks, takes place after such crooks--already positioned for engagement--have been caused to oscillate by the hooks. In the known arrangements of this type, some of the members operating the crooks--under control of the means reading the pattern of the fabric to be woven--are mounted on the same rocking shaft of the crooks, said shaft being subject, while the dobby is operating, to the stresses imparted on said crooks by the hooks. The drawback of these arrangements--especially when the stresses are particularly high and frequent, as in the case of dobbies equipping very fast looms--is to greatly reduce the precision of the controls transmitted to the crooks and thus to the heald frames, on account of the strains determined by said stresses.